Mitogen-activated protein kinases (MAP) is a family of proline-directed serine/threonine kinases that activate their substrates by dual phosphorylation. The kinases are activated by a variety of signals including nutritional and osmotic stress, UV light, growth factors, endotoxin and inflammatory cytokines. One group of MAP kinases is the p38 kinase group that includes various isoforms (e.g., p38α, p39β, p38γ and p38δ). The p38 kinases are responsible for phosphorylating and activating transcription factors as well as other kinases, and are activated by physical and chemical stress, pro-inflammatory cytokines and bacterial lipopolysaccharide.
More importantly, the products of the p38 phosphorylation have been shown to mediate the production of inflammatory cytokines, including TNF and IL-1, and cyclooxygenase-2. Each of these cytokines has been implicated in numerous disease states and conditions. For example, TNF-α is a cytokine produced primarily by activated monocytes and macrophages. Its excessive or unregulated production has been implicated as playing a causative role in the pathogenesis of rheumatoid arthritis. More recently, inhibition of TNF production has been shown to have broad application in the treatment of inflammation, inflammatory bowel disease, multiple sclerosis and asthma.
TNF has also been implicated in viral infections, such as HIV, influenza virus, and herpes virus including herpes simplex virus type-1 (HSV-1), herpes simplex virus type-2 (HSV-2), cytomegalovirus (CMV), varicella-zoster virus (VZV), Epstein-Barr virus, human herpes virus-6 (HHV-6), human herpesvirus-7 (HHV-7), human herpesvirus-8 (HHV-8), pseudorabies and rhinotracheitis, among others.
Similarly, IL-1 is produced by activated monocytes and macrophages, and plays a role in many pathophysiological responses including rheumatoid arthritis, fever and reduction of bone resorption.
Additionally, the involvement of p38 has been implicated in stroke, Alzheimer's disease, osteoarthritis, lung injury, septic shock, angiogenesis, dermatitis, psoriasis and atopic dermatitis. J. Exp. Opin. Ther. Patents, 2000, 10(1).
The role of p38 MAP kinase as a therapeutic target in oncology has been reviewed: Podar, K. H.; Teru; Chauhan, Dharminder; Anderson, Kenneth C., “Targeting signalling pathways for the treatment of multiple myeloma”, Expert Opinion on therapeutic Targets 2005, 9, 359-381; Schultz, R. M., “Potential of p38 MAP kinase inhibitors in the treatment of cancer”, Progress in Drug Research 2003, 60, 59-92.
The inhibition of these cytokines by inhibition of the p38 kinase is of benefit in controlling, reducing and alleviating many of these disease states.
Chemical derivatization of active drug moieties is frequently undertaken for a variety of reasons including modification of the physical properties of the active drug, optimization of the pharmacokinetic parameters and site-specific targeting or localization of the active moiety to specific target tissues or cells. Albert introduced the term prodrug to describe a compound which lacks intrinsic biological activity but which is capable of metabolic transformation to the active drug substance (A. Albert, Selective Toxicity, Chapman and Hall, London, 1951). While the metabolic transformation can catalyzed by specific enzymes, often hydrolases, the active compound can also be released by non-specific chemical processes. Produgs have been recently reviewed (P. Ettmayer et al., J. Med Chem. 2004 47(10):2393-2404; K. Beaumont et al., Curr. Drug Metab. 2003 4:461-485; H. Bundgaard, Design of Prodrugs: Bioreversible derivatives for various functional groups and chemical entities in Design of Prodrugs, H. Bundgaard (ed) Elsevier Science Publishers, Amersterdam 1985).